ML20203G519
| ML20203G519 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 12/29/1997 |
| From: | Douglas Dodson FLORIDA POWER & LIGHT CO. |
| To: | |
| Shared Package | |
| ML20203G511 | List: |
| References | |
| NUDOCS 9803030008 | |
| Download: ML20203G519 (33) | |
Text
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I i
i i I Attachment 2 1
Ultrasonic Examinations for Detecting of MIC In Stainless Steel Service Water Piping Virginia Electric and Power Company North Anna Power Station 9903030008 900224 PDR ADOCK 05000330. 1 P PDR .
December 29,1997 Ultrasonic Examination Technique for Detection of Microbilogically Induced Corrosion in North Anna Stainless Steel Service Water Piping Ptspared By: David R. Dodson Matl's/ISI Engineering Reviewed: M _j TMI eMAPSISI/NDE Reviewed:
Matt'sftngineering Reviewed; [U ~
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Supv. Matl's/ISI Engineering
Table of Contents I
l S:ction Topic Page 1.0 Introduction 1 2.0 Program Overview 2 3.0 Destructive Examination Results 6 I 1
4.0 Comparison of Destructive and 16 Nondestructive Exarnination Results 5.0 Analysis of Examination Results 26 6.0 Conclusions and Recommendations 30
i 1.0 Introduction f
, North Anna has been monitoring stainless steel Piping in the service water system for Microbiological l Induced Corrosion (MIC) since October,1996. To date, monitoring has been accomplished by way of walkdowns looking for visual evidence of 'eaking components followed by radiography for detection i
and length sl zing of MIC indications. Although radiography is believed to be an effective examination method, it is not an efficient way to conduct an initial evaluation of MIC. The necessity for radiation j exposure controls and the inherent slowness of the examination method limits the utility of
, radiography for inservice examinations.
i in late 1996, a Service Water Task Team was formed to evaluate the problems associated with MIC in small bore service water piping. In March,1997 the Service Water Task Team issued a report
- containing short and long term recommendations for management review. Among the long term accommendations made was a suggestion to investigate the use of Ultrasonic testing (UT) and other nondestructive examina
- !on (NDE) techniques for detection of MIC and to improve our ability to size (estimate the depth) MIC indications. It was felt that an effective UT tech-b lue for detection of MIC would allow inservice von' metric examination of service water components less intrusively and on a j larger scale than with radiography thus improving the effectiveriess of our MlC program.
! Parsuant to the preceding recommendation, a study was initiated in September 1997 to investigate
- the potential of using UT for detection and sizing of MIC indications in stainless steel service water piping welds. Sections of replaced stainless steel service water piping which had been radiographed were obtainod for development of a UT technique. Soparate sections of piping were selected for l
examination by UT and tb sse welds were destructively examined.
The results of the study led to the following conclusions:
i l 1. The U1 technique developed under this program is as effective as RT for detection of MIC but will result in omrcalls in some cases. The number of overcalls expected is not significant.
- 2. The UT length sizing technique developed under this program is as effective as RT for length sizing of MIC indications when considering the totallength of flawed weld.
- 3. The UT depth sizing technique developed under this program is capable of measuring the depth of MIC indications within 0.060" or about 18% of the average weld thickness, it is believed that sizing performance can be improved to about .040" if sizing is limited
. to indications located on the accessible side when performing sizing on single sided access welds.
I
2.0 Program Overview
- 1 Objectives
- 2. Verify the results of the UT technique by destructive examination.
- 3. Verify the effectiveness of the UT technique in comparison to radiography by relating the results obtained on the same weld samples.
8:mple Selection MIC attack has been experienced in 2",3" and 4" stainless steel service water piping welds at North Anna. The 2" service water welds are socket welded and therefore are not suitable for UT. There was nc 3" diameter piping available when samples were being selected for this program, however, UT technique parameters were developed for 3" piping using Virginia Power's Appendix Vill piping specimens. The majority of the butt welded joints that have been confirmed to contain MIC at North l Anna are on 4" diameter lines.
To the extent practical, the sample set was selected to meet the fabrication conditior,s specified by !
Appendix Vill of ASME Section XI for austenitic piping welds. The sample set consisted of ten welds which were selected from three different servico water lines. In order that a blind UT test could be p;rformed on the welds, a separate set of welds was used to develop the UT technique. The sample i
s;t included welds with wide weld crowns and welds with pipe fittings that permitted only single side cccess for UT. All welds in the sample set were as-welded which prevented the UT transducer from b3ing scanned over the weld. The welds contained areas of root convexity, root concavity, and v:rious welding defects. All welds in the sample set were made from 4" diameter standard wall stainless steel piping. Weld metai thickness measurements were made on the specimen set during dcstructive examination which showed the thickness over the sample set to range from .285" to
.375". Five of the ten specimens selected for this program (FW 19W, FW-13, FW-16, FW-61 and FW-
- 64) showed evidence of leakage in the field.
The weld numbers that were selected for the specimen set are listed on Table 1:
Table 1 Drawing Line Number Weld Number WS 16D 4' WS 57163-03 W 19W WS-16E 4'-WS-57 163-03 W 1W WS 19F 4* WS-46163-03 FW 94 WS 2D87A 4*-WS-F63 163-03 FW 13 WS 2D87A 4* WS-F63163-03 FW-14 WS-2D87n 4* WS-F63163-03 FW-16 WS-2D878 4*-WS-F63 163-03 FW-61 WS-2D87B 4* WS F63163-03 FW-63 WS 2007B 4' WS-F63163-03 FW-f4 WS-2D878 4" WS-F63163-03 FW 78 2-
R diography Eight of the above specimens were radiographed in the field and one additional specimen was tcdiographed after replacement. A double wall single viewing radiographic technique was used. FW. .
l 14 above was not radiographed.
UT Technique The morphology of MIC within a weld often presents a challenge for detection and sizing when using st:n jard angle beam ultrasonic techniques. MIC often exists within a weld as a group of elongated voiu which may enter the ID surface adjacent to the weld root and meander along or through the vnd oxiting the OD surface at an entirely different location. MIC also tends to occur in clusters which rcsNs in a network of randomly orientated " worm holes" within a weld. This morphology does nat procent an optimum reflecting surface when using standard angle beam techniques. It was felt that a UT technique that insonified a large percentage of the weld volume would be needed to reliably d:tect MIC.
The UT technique that was developed consists of two examinations. The first examintaion utilized a 2 MHz dual element ADEPT tandem (ADEPT-60) search unit. The elements of the search unit are mounted front to back with a short sound exit point which allows a closer approach to the weld toe.
The search unit introduces two sound modes (L-Wave and shear) into the specimen. The dual sound modes intenogate both the ID surface and volume of the weld being examined. On very thin material, such as the specimens in this program, the search unit essentially insonifies the entire volume of the m terial being inspected. The L Wave component of the sound beam easily penetrates austenitic wald material resulting in a relatively high sensitivity to MIC. The ADEPT 60 is used for detection and h:ngth sizing of MIC indications. The second examination utilized a small diameter 45 degree shear wcve search unit. The 45 degree shear wave examination it used to further interrogate the Indications detected with the ADEPT-60 in order to discriminate inherent welding defects, such as incomplete fusion, from MIC indications and for through wall i ig.
Following devclopment of the UT technique, blind examinations (without access to radiographic or other information) were performed on the ten specimens in this program. Radiographic results were rcviewed before the specimons were destructively examined.
l Doctructlve Examination Following UT examination, the ten specimens were destructively examined, it was first r'anned to s:ction the specimens into quadrants and remove cross sectional slices of material by grinding small increments of material, however, this process proved too time consuming. Only one of the specimens (FW 14) was processed in this manner, FW 14 was chosen as the first specimen to destructively cxamine because the UT examination revealed no indications in the specimen and it had not been rcdiographed, This specimen was not dissected completely across, however, it was examined to the cxtent necessary to determine that th' was no evidence of MIC or other indications of significance in the weld.
3
( The 9 remaining specimens were fashioned into coupons by cutting through the base metal l perpendicular to the axis of the pipe on each side of the weld. The coupons were then law,orted int 0 a lathe and cut in .020" increments perpendicular to the axis of the coupon. Observationr were made after each cut and the results were documented after every three cuts (.060"). The results for each
" Group" of three cuts was labeled on the documentation with the letter *G" followed by a sequential j number (1,2,3 etc.) that relates to the progression of cuts through the coupon.
The niethod of processing the final 9 specimens tended to slightly smear the metal on the machined surface of the coupon. The resulting smeared metal resulted in a potential to obscuro very tight weld imperfections such as incomplete fusion and shallow conditions at the weld root. However, MIC was the primary focus of the destructive examination and it is believed that this method of processing effectively revealed all evidence of MIC that was of any significance.
A photo of FW 94 mounted in the lathe is shown on Figure 1. The photo clearly shows nodules on the ID of the 71pe which are characteristic of MIC attack. Figure 2 shows a close up of a vold in the base metal of FW 94 caused by MIC attack. The same void is also visible at approximately 1 o' clock on Figure 1.
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3.0 Destructive Examination Results in order to better show the destructive examination results, cross-sectional sketches were made which graphically depicted the locations of the indications observed. A cross section view was drawn which represents the results for each group of cuts (i.e., each 0.060" s, lion). Each view sho vs the circumference of the coupon laid out flat. The views for each group of cuts (G1,G2, G3, etc.) are aligned under one another on the same page to relate the coordinates of each subsequent group to the preceding group. These views allow one to visualize the progressive circumferential and through-wall distribution of MIC along the axis of the coupon. A composite cross section view representing the cumulative results of all the cuts made on the coupon was developed to serve as the basis for h comparing the destructive results to the NDE results.
The destructive results revealed evidence of MIC as well as other indications such as porosity and weld inclusions. It is often difficult to differentiate MIC from other indications by visual exam! nation alone, however, it is easy to determine if an indication progresses toward the ID surface by s comparing views from successive cuts. Since MIC always originates at the ID surface, indications which clearly do not progress toward the ID during subsequent cuts are accumed not to be MIC
}
Figuros 3 through 11 depict the results of the destructive examinations for all the specimens listed on Table 1 with the exception of FW 14. The results for FW-14 are not shown because no indications of significance were observed in this weld during the destructive examination.
Figures 3 through 11 reveals the following regarding the nature of MIC in the NAPS stainless steel Service Water piping:
1 In Type 316L SS Welds, MIC appears to be primarily restricted to the weld and the portion of the heat affected zone which is immediately adjacent to the weld. Only one coupon (FW-94) contained MIC which was located in the base metal outside of the weld.
- 2. MIC appeau to form in clusters which should improve the probability of detection by UT. When several clusters exist they tene: to be randomly distributed around the weld circumference.
- 3. Very deep MIC indications appear to occupy a substantial volume of space within the weld which should improve the probability of detecting them with UT.
6
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15
4.0 Comparison of Destructive and Nondestructive Exammation Results in order to facilitate comparison of the destructive and nondestructive examination results, sketches ware made from the NDE results. The sketches depict the weld laid out flat showing the circumferential location and length of each indication detected by the NDE method. The NDE sketches for each weld are shown on Figures 12 through 20 aligned under the composite cross-section view of the destructive results for each respective weld. Clusters of MIC shown by the destructive results are grouped as a single indication since clusters of MIC are reported as a single indication by NDE. In areas of dense clustering, a supplemental plan view was made of the destructive results to show the distribution of MIC across the weld.
Some displacement of the location of an indication between the different results should be expected.
Displacement in location can primarily be attributed to variations such as differences in the layout of the weld, differences in measurement accuracy and blowing of indications caused by geometric factors during radiography. (Blowing of indications on radiographs is more pronounced on small diameter piping for indications that are located nearer the edge of the film).
Small volume weld defects such as incomplete fusion which were detected by both UT and RT are assumed to be real indications that were not reported during the destructive examination. UT indications that were not detected by either destructive examination or RT were assumed to be overcal;s. Small volume weld imperfections such as porosity and inclusions were observed during ,
the destructive examination. Such indications were not considered to be missed detections since they would not have been a factor in acceptance of the weld.
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- 21a-(8)
Radiographic Results Circumferential Location 0" 1" 2" 3" 4" 6* 6" 7" 8" 9" 10" 1'" 12" 13" 14" 14 600" L-~__... -
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7 _ . MIC ,
Note: *A single Indication would be called from 3" to 12" 19
i 1
i
~ Figure 15 4" WS-F63163 03 FieldWeld 13
- MetallurgicalResults
- . Cross Section View
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Figure 16 4" WS-F63-163-03 FieldWeld 16 MetallurgicalResults Cross SectionView
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1 MIC 2 2 2 MIC 3 NA -NA _ Porosty
(' 4 NA NA Root Artifact o 4 3 pjC l 6 miss 3 MIC l 7 -5 3 MIC i
_ l'% 3(OC)_ NA IF 21
4
- Figure 17 4"WS-F63163 FieldWeld 61
- MetallurgicalResults Cross SectionView r r r r c r r r r r ir ir it ir ic 34ser "b }_
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d NA Poros_t _
NA 3JOC) NA L _ IF 22
Figure 18 i
, 4" WS-F63163-03 Field Weld-63 i
MetallurgicalResults Cross SectionView
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Destructive ' LET RT Ty 1 1 1 1 MIC 2 1- 2 MIC 3 4 6 MIC
[ NA NA 3 Porosity l NA 2. 4 MIC NA 3 5 MIC _
23
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Figure 19 4" WS F63-163 03 Field Weld-64 MetallutgicalResults .
Cross SectionView 7 r r r r r r r r r it it ir ir ic $4w 4
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l Figure 20-4" WS-F63-163 FieldWeld 78 Metallurgical Results Cross Section View
, y 1* - 7 y 4- 5* C T - 8* r 10' 11* 1T 1r 14* 14 600"
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- /Tr Ultrasonic Results Circumferential Location l
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5 Called Incomplete Penetranon Radiographic Results j Circumferential Location 5 y t* r y 4a 5* 6 T 8' r 10' 11* IT ty 14* 14 600'
~ - -- . . ." - - . ~ - - . .
, .t - 2 r* t-- '*4'" '8* '1 * -i- 'r* *1" 0 irr ' O14' O14 0 SS*
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-l Inslocatten # s trad6 cation -
- Type 1 1 2- 2 1 MIC
-2 3 5 MIC 3
[ miss miss - MIC 4 4 6 MIC 5- NA NA Porosity NA i 1 1 IP
- N_A { NA* 3- _._. Porosity NA l NA* 4 - Porosity Nf. ' i NA* 7 Corcsity NA i NA* 8 Root
- NA . ! NA* 99 If[Concavny)
Note: 'Noted on UT report but not r. *sidered recordable
- RT indication #9 appears to L onca. ty upon re-review -
25 L--- -----__.___1__._, _. -m - ,, ..r- - . m.- ,,m ,_ - .m.., ,,,.
.- . - =-. -_ - - -=- - . -
Analysis of Examination Results Th3 primary objective of this program was to develop a UT technique which would be comparable to RT for detection of MIC and which could also provide a reasonable estimation of the lerigth and through wall depth of MIC indications. In order to measure the success of this objective, it was felt that a standard for comprison of results was needed which provided performance criteria for 3
detection and sizing of indications.
Appendix Vill of ASME Section XI provides rules for detection and sizing of indications for inservice ultrasonic examination of nuclear components. Appendix Vill is intended to apply to detection of cracks in specimens which were designed and fabricated to prescribed conditions. The specimens selected under the program described by this report represent real inservicc conditions. They do not contain cracks and could not be selected to meet all of the design requirements of Appendix Vill, especially those seleted to flaw distribution. However, it is felt that the performance criteria of Appendix Vlli can be applied to this program provided that reasonably unambiguous results are obtained. This entails including Specimens which contain specific isolatable areas which can be reporied as flawed or unflawed. It is felt that the reported results for the specimens in this program gencH.lly meet the preceding requirements with the exception of FW-94. In order for FW-94 to be
! properly evaluated, the area from 3" to 12" would have to be considered as a single indication.
4 D tection An issue associated with the evaluation of these results centered around the disposition of incomplete fusion (IF) which was not detected by the destructive examination. Three basic cases could exist evolving the preceding:
- 2. IF detected only by RT, and ;
- 3. IF detected only by UT.
Case 3 above was considered an overcall even though this classification is considered to be very conservative, it was ciso felt that a miss by UT should not be recorded when indicatior.s were detected only by UT as in the case of 2 above. A good argument can be made that UT should be more sensitive to small areas of incomplete fusion than RT. Also dae to its similarity to light slag inclusions and various root conditions, incomplete fusion is often incorrectly interpreted by RT. As it turned out, there were no cases like 2 above but there were 5 cases like 3 above.
This program was primarily geared to detect MIC indications, however, weld defects which are unacceptable in accordance with ASME Section 111 are also considered in the structural integrity evaluation of service water welds, in order to better assess the ability of the UT prccedure to detect MIC indications, it was decided to break down the results into categories of MIC + Weld Defects and MIC only. Only weld defects which were considered to be unacceptable in accordance with ASME S ction 111 were required to be detected (that is, acceptable indications such as porosity and inclusions are not included) .
26
l
- l.
Table 2 below summarizes the detection and overcall performance achieved for both UT and RT on tha specimens in this program. The detection and overcall criteria shown on Table 2 is derived from Tcble Vill S21 of Appendix Vill. Table Vill-S2-1 only accommodates up to 20 flawed grading units in a specimen set. The minimum detection criteria on Table 2 was calculated based upon the ratio of tha minimum detection criteria to the number of flawed grading units from Table Vill-S2-1 for 20 flawed grading units The overcall criteria on Table 2 is based upon 40 unflawed grading units, which is very conservative.
Tablo 2
.E 784.T : 7) & J fJ:. MIC Onlyb l: ; : R '. X ' 1.h 1'
Method Flawed
- j Detections i Overcalls Minimum Req. ! Overcalls l
j Gradjng Units I . __ _ _.
Detections , _ Allowed RT l 37 33 0 i 26_. _ 8 i UT ! 37 33 1 26 8 !
7- - . . ,
~3.' Y
. IC + W el4 04fects i ' C* d ' 7 Method Flawed
- Detections Overcalls Minimum Req. Overcalls
__ Grading Units , _ ' _ . Detections _ Allowed _ i
_.0 RT .40 35 28 .8_
[UT ii . _ _ _ . [4'0 _ _ _ . . _ _
'36 [__ _ _
6 , _ _ _ [2 8 } ~ ~ ^
j8i Note:
- Area from 3" to 12" on Figure 14 was considered as a single M C indication.
Table 2 shows that UT will detect MIC as effectively as RT but will most inely result in some additional indications being called. The detection performance achieved by both UT and RT is well above that specified by Appendix W for qualification of a detection procedure. Review of Figures 12 through 20 shows that only MIC with a small cross section area was missed by UT. The deepest ,
area of MIC missed by UT was about 37% EN (Indication # 3 on Figure 12).
Length Sizing This section deals only with sizing of MIC indications. Accurate length sizing of MIC is an important consideration when evaluating the structural integrity of a component. The criteria used to assess structural integrity is the total length of MIC in the weld . Since MIC often occurs in clusters, it is often difficult to precisely determine the length of individual segments of MIC nondestructively. Table 3 below lists the length of each MIC indication identified by the destructive examination along with the ;
corresponding RT and UT results for each indication. In general, the indications documented on Table 3 are the same indications shown by Figures 12 through 20 for the destructive results, however, in some instances the length of indications are combined due to their close proximity.
Indicat;ons which are combined are also combined under the heading " Destructive Resuks Length by Indication #". Only the indication numbers which correspond to the destructive results are identified on Table 3. The corresponding indicc' ion numbers for RT and UT can be determined by referring to the individual tables under Figure 12 through 20.
Appendix Vlli requires that all' laws be sized within 1" of their true lengths. The flaws included in this program are generally very shod which makes the Appendix Vill 1" allowance seem overly liberal when applied to individual flaws. However, it seems adequately conservative to apply the 1" criteria 27
to the total length of flawed weld which is the primary criteria for determining structural integrity.
Also, by applying the criteria to the total length, overcalls and undercalls are factored into the length which provides a more accurate picture of the performance of the NDE method. As can be seen by Table 3, both RT and UT would meet the Appendix Vill length criteria when considering the total 1:ngth of flawed weld. True flav length is considered to be the length c'etermi. led by destructive examination. When considering the totallength of flawed weld, the maximum deviation from the true I:ngth for UT is .659", with the average deviation from true length being .259". This is comparab!e to RT which has a maximum deviation from true length of .845", with the average deviation from true length being .387".
Table 3 g .
..u.. .- .. '7.--
. :p gg g; . : ..f-r-
' yg
. , .. so . , . . . . ... r. ~. . . , ,o 828 i 0 78 t_ i
- . _ _ --_.i -
! . _W_19_W. .___ _DE S T. j _.156._ _ !
a ._.078 -
i i _ 1140.q' !
__ _7 _
-. - _ . _ . , ,_._._-g-_-- --_-__ _ - p _ _ ,
M'M N W1..-W, -
DEST._4_ 062_ NA. .
~
.. 656 ,_ _125 . 406 . 812 - e- 312.-.! -.094 -----__{ .- _._.. 2 46 7 _q i
- ~ ~ ~
~ uT ~ t ~ 1250 ' ~ 625~ ~~ 375'~ 7 .375~ ^ ~625 625 '250 " ~ ~ ' t ~ ~ ~ ~ 3 12 5 :
M, :g
. 7.. g- .
'g; ..~ .y- '). .g ?g' .
gg .. . . -
l - FW 94 - i DEST ! 344 ~~
8' ~~~ ~
I 8 344
- ~~'~ ~ ~~~ ~
8 (MiC.oniy 4" 12*) ~~ ~~ ~ ~ ~ ~ ~ ~ ~]8375 ~ ~~ e p _-- - _ T R I ~'_ 375~ _
9 ,. g . g EFL FW-13_ J , DEST .4 562_ j _ _ 437 375 _.] _.125 ._. 312 ; __.12 5 _1 312 _j. ;094
.J{..32187 342.! _ j
_ j .._ RT 4 750 _ _
250 ,_ __ . 375. . ,) - NA . _ 250 ,. _. 375. -, _ -.375 . y; - .812 i i
., 9 FW 16 .312 NA 469 . 437 t 1 499 1
,g _ . 5g, 219_ i ! i
_D.EST_ . l
.__-.__ _ .. g - .. . - - _NA__ !__ _
t.
062 --. . NA-
..A. ,' l - ~I.~_2 062' ",
U n ' m M.R?
! ~ fW-61 D T _. 562
_625_[. _ _ _ . , _ _
__g______.___ _ _ _ _ _ _ _ , _ .
. __ _FW.6_3, _ i . DES T . f.-.__.218 -.'_. 218.-.i _.094 , . _ . _ _ . _ _ _ _ _ _ . _ _ _ .i _ _ __ ! ___i._ { .530 i
..' ~ ~ ~T ~ ~ ^ I ~~ ~ I~
~ ~
'I-~UT ~ l 500 7 N. A
.. .125. .
i
~625~
l FW-64 DEST NA NA
! t 062 1 937 i 399 {
NA ~{ ._.2 50 . _ .._.i _ _ _ ,_ . ,i_ _ _ 2507
[_ _ . .RT _ . . . - _ . _ _
i ! ,031 625 .125 .375 l ? i j
.i .1.156
_FW-78_7. DEST 7
- r- _
, [ UT_ t .500 .375 NA .500 J ! 1
! i 1.375 l Depth Following the detection and length sizing examination of the specimens in this program, through wall d:pth measurements were made on a sample of the indications detected. The through wall measurements documented on Table 4 represent the measurements taken on the indications 28
confirmed to be MIC by the destructive examination. At least one area of MIC was measured from e ' .h of the specimens which contained indications. The indication numbers shown on Table 4 correspend to the indication numbers shown by Figures 12 through 20 for the destructive results.
Table 4 1
! Ehd M e
[
W 19W .-._.! .-.-.-1 1
_..-0 098 . - _ 6 0 095 i 0 000009 _
-w. mv. .._. . - . i . . .-. 4 . . _ - - . - _ _
c- 0138_-_-T. .~._._ 0.iOO---.i .
0 00i444 .
i i . _ . _ . . . - -
q W1 W _ . _ _ . . _ i_. _ _-__7 _ _ T -- _.-.- .. _.0 i 96 _ __ __. . i _. _
i 0"00096i ~
0165.-__--_ _ q
. - . ~ _
__...__.7_
i
[TT FW 13_.,__ ,_L.,__1 ._____[.,_. ~ 0'107 0 170 _ _ , ~6003969 _]
t FW.13 ! 3 0 277 .
_ 0276 _ __q 0 000001 J I_ ..__ FW-13 ,_ __q . i
_.5.__..._
__ _ 0 097 . _ . l __ 0100 __ _ q _. 0 000009 !
FWi3 I 7~ ! ~O 375 i 0370 i 0000025 l 1---~~ ~8
~
_ . _ FW.13 j__________ __
I 01'4'6 ! 0365~ _ T - ~D047961~ ,
___FW 16 1 4
^-7 i q__ _0 j.82- 0D j~ 0"100- ! 60dd324 ~i 95 ! 0150 003 25~~~ l
~ ~ ^ ~FW-63~ ~ [ ~ ~ ~ l&2 ~~ ~ ~U }0 I96 ~i- ~ ~~ 0'80 1
))~ __0'000256 ]
FWW i 3 O137 .,J5 0 002704 i J 137 0 080 00032d9 l
__FW-C . {~~~~~~ ~ 3 i !
j . . . FW* .__-I 5 ! 0280-- - - _ 0 255 '
0000625 :
]
gw,73 p _ 7_. _- _ _ _,I _ 0 283 i 0'2_73~~ ~ I~. _ _ .
~ __ _0 000144 y
._ ___ _____ m _ . . . _ _ _ . _ _ .
j j = 0 060" RMS=\ n Apper. dix Vill to ASME Section XI allows an RMS error of 0.125" under Supplement 2. Because the average thickness of the weld metal for the specimen set averages about .330", the RMS error specified by Appendix Vill does not appear to be adequately conservative. However, the RMS error actually achieved is a little better than twice that required by Appendix Vlli. The RMS error achieved
(.060") is abou+ 18% of the average weld thickness of the sample set wh ch corresponds to an RMS ;
error of .125" on a specimen set with an average thickness of .700". l Four of the indications on Table 4 (FW-13, Ind.#1, FW-13, Ind.#8, FW-16, Ind.#5 and FW-61, Ind.#1) were significantly undersized. Review of the NDE reports for these welds shows that all of the preceding welds were made to 90 degree elbows and that indications were located near the intrados of the elbow. These welds are single side access in the area of the intrados and it is believed that the geometry in that area resulted in errors in the depth estimate. It would not be recon'r.iended that sizing be permitted on indications like those above. If the preceding indications were not included in the sizing estimate, the RMS would have been .040" or about 12% of the average weld thickness.
29
, - . . ..e.. < , . .
t 6.0 Conclusions and Recommendations Can:lusions Tha results achieved by this' program provide the basis for the following conclusions:
- 1. The UT technique developed under this program is as effective as RT for detection j of MIC but will result in overcalls in some cases. The number of overcalls expecMd is not significant.
l 2. The UT length sizing technique developed under this program is as effective as RT for l length sizing of MIC indications when considering the totalleng'h of flawed weld.
- 3. The UT depth sizing technique developed under this program is capable of measuring the depth of MIC indications within 0.060" or about 18% of the average weld thickness.
It is believed that sizing performance can be improved to about .040"if sizing is limited to indications located on the accessible side when performing sizing on single access welds.
Recommendations
- 1. NAPS should consider UT for monitoring of MIC in stainless steel service water piping.
It is believed that the use of UT will prove to be an effective examination method that is less intrusive than RT.
- 2. If a UT program is to be implemented, UT personnel should be qualified for detecticn or sizing, as applicable, of MIC indications as a prerequisite for conducting examinations. Also, the UT personnel should receive at least 40 hours4.62963e-4 days <br />0.0111 hours <br />6.613757e-5 weeks <br />1.522e-5 months <br /> of hands-on training utilizing service water piping that has been removed from service prior to performing an examination in the field.
- 3. If through wall sizing of MIC ia to be performed with UT, it should not be conducted in those cases where the MIC is located on the inaccessible side of single sided access welds. ,
- 4. If UT is used, the UT results should be periodically validated with RT or destructive examination on a small population of welds. It is believed that two or three welds wnich ,
were examined by UT should be selected and examined by RT or destructive examination on an annual basis.
30